A video communication system such as, for example, a television communication system, typically comprises an encoder, a transmission medium and a decoder. Such a system receives an input video signal, encodes said signal by means of the encoder, transmits the encoded signal via the transmission medium and then decodes or reconstructs the transmitted signal by means of the decoder, resulting in an output video signal. A video signal represents a given number of images, an image being associated with a time slot t.
Before transmitting video signals, a video communication system may include a video compression process. Such a video compression process is sometimes performed at a low bit rate in order to transmit more video signals. It produces significant distortions in an image of a video signal, especially visual artifacts such as blocking effects (tiled effect aspect), ringing (ghost aspect) or mosquito noise (flying swarm of mosquitoes aspect, i.e. a flickering effect). As described in “Adaptive Postprocessor to reduce Temporal Business in Low Bit Rate Video”, at the Picture Coding Symposium 23-27 Apr. 2001 written by F. X Coudoux, M. Gazalet and P. Corlay, a solution to reduce the mosquito noise is to separate non-edge blocks from edge-blocks within an image corresponding to said transmitted video signal, said image comprising blocks referred to as DCT blocks, well-known to those skilled in the art. This solution applies a temporal DCT median filtering on the non-edge blocks. Said temporal median filtering comprises the steps of:                computing a temporal gradient between AC coefficients of three DCT blocks of three consecutive images, respectively, in order to look for discontinuity within said images,        by way of a threshold, looking for sudden temporal transitions such as fast motion objects, and        if there is a local discontinuity and no sudden transitions, applying a temporal median filtering on said blocks.        
One problem of this solution is that it only reduces the mosquito noise on non-edge blocks within an image of said transmitted video signal, whereas mosquito noise can also appear on edge-blocks.